# LBM for a compression of high density ratios

Dear LBM-community,

I am a beginner at LBM, but I want to use it for my Phd.

I want to find out if LBM is suitable for my application and want to use it for a simple case.
It is just a gas filled volume with bounce-back boundary and than I want to compress is by continously decreasing the volume. At the end I want to get a density ratio of around 1:10.
Do you think it is possible to do it with LBM?
How shall i implement the compression, using imersed wall algorithm or a sudden density change of the dynamics of the grid?

Do you also have any advice on the fluid model as well? Which model would you use for this kind of application?

I am looking at thermal expansion of solid inclusions and had a similar (though less extreme) question. I implemented a test model in 2D of a square domain with an expanding cylinder in the middle. if the fluid volume decrease is small, say 5%, the error in fluid pressure is equally small at approx. 3%. This is acceptable for my purposes.

I just did a test with the model, for a 75% reduction in fluid volume, the error in pressure is approx 140%.

This model uses BGK LBM with the immersed boundary condition of Noble and Torzcynski. For the expanding cylinder all I did was set the velocity of boundary nodes to reflect the expansion velocity.

For youâ€™re purposes I think you will need a more sophisticated approach. I think my model is a bit of an abuse of the weakly compressible assumption, you would need an LBM algorithm designed for compressible fluids.

Bruce

Thanks a lot for this answer.

I will follow further devolpment of LBM and skip this problem for now.

Greetings Fabian